1. Field of the Invention
The present invention relates to a prosthetic foot that simulates toe rotation. More particularly, the present invention relates to a prosthetic foot having two separate members forming opposite halves of the foot generally about the longitudinal axis of the foot or having a substantial longitudinal slit formed in the foot.
2. Prior Art
Many individuals have lost a limb for various reasons including war, accident, or decease. In most instances these individuals are not only able to live relatively normal lives, but physically active lives as well. Often times, these is individuals are aided in their everyday lives by a prosthetic limb. The objective of prosthesis is to provide an artificial limb that simulates the function and natural feel of the replaced limb.
With respect to prosthetic feet, the development of a functional and natural artificial foot has been limited only by material and imagination. Many designs have attempted to copy the anatomy of the foot or simulate its actions by replacing the bones and muscle with various mechanical components. Other designs have departed radically from mere anatomical copying or mechanical simulation by replacing the entire foot with an energy storage element such as a spring. As the user steps onto the foot, the user's weight compresses the spring. As the user moves forward, the user's weight comes off the foot and the energy stored in the spring is used to propel the user forward.
Almost all of the past designs have focused on the major aspect of the prosthetic foot--movement of the ankle or foot as it relates to walking or running. Few designs consider the workings of the toes or the less conspicuous movements of the foot and ankle, such as the rotation of the foot and toes when the user stands on an incline. In a natural foot, the foot and toes rotate to conform to the slope of the terrain. The artificial foot of previous designs usually incorporates a unitary foot and toe platform that is incapable of such independent rotational movement or response.
U.S. Pat. No. 5,037,444 issued Aug. 6, 1991 to Phillips discloses a prosthetic foot having a forefoot portion and a heel portion. The forefoot portion has an attachment section, a curvilinear spring section, an arch section, and a toe section formed integrally with one another. The heel portion is removably attached to the forefoot portion at the intersection of the arch and toe sections by a bolt and nut. An elastomeric wedge is inserted between the forefoot portion and the heel portion.
One problem with this configuration is that the forefoot portion, together with the heel portion, form a unitary member incapable of providing independent and multiple responses to uneven terrain, such as a slope. The unitary member is a platform that must rotate as a single body to conform to the slope of the terrain in an unnatural manner. Such a foot is incapable of rotating about a longitudinal axis.
In addition, the forefoot portion and heel portion are attached by a bolt and nut through a bore. Such a bore in a structural member or spring member causes stress concentrations in the material which can lead to catastrophic failure.
The heel portion acts as a lever. When in use, all the weight of the wearer is placed on the heel as the users steps forward. The elastomeric wedge, or the contact between the heel portion and the forefoot portion, acts as a fulcrum at a position between the two ends of the heel portion. Yet the other end of the heel portion is bolted to the forefoot portion. Therefore, a large stress is caused at the connection end of the heel portion which is concentrated at the bore and may break the heel portion.
Furthermore, a shear stress is placed on the bolt because the forefoot and heel portions tend to slide with respect to each other. The tendency to slide also concentrates the force applied by the user (static weight and dynamic walking) in the small area around the bore.
Finally, the attachment section of the forefoot section is a plate with a centered bore. There is no structure or means to adjust the angle of the prosthetic foot with respect to an ancillary socket or the angle at which the prosthetic foot contacts the ground.
U.S. Pat. No. 4,547,913 issued Oct. 22, 1985 to Phillips discloses a prosthetic foot having a forefoot portion and a heel portion. The forefoot portion and the heel portion are bound together with a "resin impregnated filament binding" by winding the filament around the members. Problems with this type of joining technique are (i) the lack of strength in the connection to resist shear forces and (ii) the vulnerability of the connection to shear stress The real strength of fibers is their tensile strength, or the strength of the fibers under loads along the length of the fibers. Thus, filaments circularly wound around two members would be most successful in resisting tensile forces pulling the two members apart. The filaments would be less successful in resisting shear forces sliding or twisting the two members apart Because the foot is subject to so many different forces in many different directions, it is critical that structural or spring members be attached by a method capable of withstanding the numerous applied forces.
U.S. Pat. No. 2,640,200 issued Jun. 2, 1953 to Wisbrun discloses a prosthetic foot having a steel, horizontal foot plate connected to a vertical leg post by two joints. The first joint has a head mounted in a diagonally mounted cylindrical bearing such that as the foot plate rotates downward it is also rotated inward and vis versa. The second joint permits limited vertical rotation by a T-head inserted through a slot, turned, and secured by a screw. An arm, attached to the leg post, extends over the foot plate and engages an inclined leaf spring. The purpose of the above construction is a more natural gait. The resulting motion of the above construction is the rotation of the foot plate down and inward as the user steps on the heel and then rotation upward and outward as weight is taken off the foot plate. Wisbrun also discloses that a slit may be provided in the forward end of the foot plate for "a more effective resilient up-thrust" as weight is taken off the foot plate. One problem with this configuration is the complexity of the several joints. There are numerous moving parts and joints subject to friction, wear, and failure In addition, the slit in the foot plate does not simulate toe rotation.
U.S. Pat. No. 2,036,830 issued Apr. 7, 1936 to Rowley discloses a prosthetic foot having a shin member connected to a foot member by a bearing hinge. The foot member has a solid, inner core portion and a flexible exterior. The foot member also has a rigid member with a "pair of spaced apart prongs" extending between the core and the exterior and a pivot at the ball of the foot in contact with the prongs. The rigid member is operatively attached to a rubber block that expands and contracts between the shin member and core member as the user walks. Thus, the rigid member acts as a lever extending from the toe position to the ankle position and pivoting at the ball of the feet. As the user pivots forward on the foot, the rubber block is compressed and the ankle end of the rigid member is forced down and the toe end of the rigid member is forced up. As the user lifts the foot, the rubber block expands and the ankle end of the rigid member is forced up and the toe end of the rigid member is forced down. The purpose of the rigid member is to return the flexible toe portion to its normal position after being bent upwards by walking. One problem with this configuration is that the rigid prongs do not deflect or bend to simulate toe rotation. Nor do the rigid prongs pivot independently.
Therefore, it would be advantageous to develop a prosthetic foot capable of simulating the natural toe rotation of a real foot. It would also be advantageous to develop a prosthetic foot having a connection between the forefoot member and heel member capable of resisting sliding and twisting. In addition, it would advantageous to develop a prosthetic foot with a means of adjusting the angle at which the foot contacts the ground.